1. Field of the Invention
The invention relates to an arrangement for recording on a record carrier an audio signal comprising a left-hand and a right-hand channel, which arrangement has a first and a second input terminal for receiving the left-hand and the right-hand channel respectively, said first and said second input terminal being coupled respectively to a first and a second input of the recording unit to record the signals applied to its inputs on the record carrier.
The invention also relates to a record carrier on which an audio signal has been recorded by means of the arrangment in accordance with the invention.
2. Description of Related Art
Arrangements of the type defined in the opening paragraph are known in the form of magnetic tape recorders, for example RDAT or SDAT recorders. In both cases the audio signal is digitised and is subsequently recorded on the magnetic tape. For this purpose an RDAT recorder employs a rotating head and the audio signals are recorded on the record carrier in adjacent tracks which are inclined relative to the longitudinal direction of the record carrier. In an SDAT recorder the digitised and encoded audio signal is divided among a plurality of stationary heads and is recorded on the record carrier in an equal number of tracks which extend in the longitudinal direction of the record carrier.
For a comprehensive description of the two above systems reference is made to the book "The art of digital audio" by J. Watkinson, Focal press, London, 1988.
One of the reasons why the systems have not yet found acceptance on the market is the problem of unauthorized copying. For this reason suppliers of prerecorded record carriers are not willing to supply such record carriers for use in one of the said systems.
Digital copying, i.e. direct copying of the digitised and encoded audio signal without prior D/A conversion and subsequent A/D conversion, hardly leads to a degradation in quality in said systems. Therefore, it is envisaged that digital copying will assume large proportions, resulting in a substantial loss of royalties.
In the past proposals have been made to inhibit digital copying. These proposals are based on the insertion of a copy-protection code in the subcode of the digital data stream as recorded on the record carrier.
Copying is inhibited upon detection of the copy-protection code in the subcode. The advantage of this method is that the audio signal is not disturbed because the protection code is not inserted in the audio signal itself.
Copying prerecorded record carriers via the analog path, i.e. the audio signal to be reproduced is first D/A converted in the reproducing apparatus and is subsequently applied to the recording apparatus in analog form, where it is re-digitised prior to recording, cannot be preluded in this way.
Since this (analog) method of copying prerecorded record carriers by means of the above systems neither leads to any substantial deterioration in quality it is also envisaged that analog copying will be used on a large scale.
Proposals to inhibit copying by analog methods have also been made in the past. For example, there has been a proposal by CBS to feed the audio signal through a very narrow-banded band-stop filter prior to recording of the signal on the record carrier. If during subsequent re-recording of an already recorded audio signal it is detected that there is no signal content in the relevant frequency range, the signal apparently concerns copy-protected information and recording is interrupted or the audio signal to be recorded is disturbed.
A drawback of this method is that the audio signal is distorted because it is fed through the band-stop filter. This distortion is sometimes audible, which is very annoying.